High speed printer



HIGH SPEED PRINTER 5 Sheets-Sheet 1 Filed May 1. 1961 INVEI'VTORSI ATTORNEYS.

N. IRW

HIGH SPEED PRINT Filed may 1961 5 Sheets-Sheet 2 T v New W M W/NVEMTOQ'Z;

W fwfi y Br 6% m ATTORNEYS.

April 30, 1963 s. N. IRWIN ET AL 7,

HIGH SPEED PRINTER Filed May 1, 1961 5 Sheets-Sheet 3 ATTORNEYS.

P 1963 s. N. IRWIN ETAL 3,087,421

I HIGH SPEED PRINTER Filed May 1. 1961 5 Sheets-Sheet 4 ATTORNEYS.

April 30, 1963 s. N. IRWIN ETAL HIGH SPEED PRINTER 5 Sheets-Sheet 5 Filed May 1. 1961 United States Patent 3,087,421 HIGH SPEED PRINTER Samuel N. Irwin, Grosse Pointe Woods, and Frederick E.

Booth, Jr., Birmingham, Mich., assignors, by mesne assignments, to Data Products Corporation, Culver City, Calif., a corporation of Delaware Filed May 1, 1961, Ser. No. 106,710 8 Claims. (Cl. 101-93) This invention relates generally to electrically controlled high speed printing devices, and more particularly to a new and improved magnetically operated hammer assembly for use in such printing devices.

It is known in theart to utilize type wheel printers wherein alphabetic and/or numeric characters are provided in columnar fashion around the periphery of a continuously rotating type drum. In such type drums of the past, a print hammer is associated with each columnar ring of type characters such that the hammer will strike a predetermined character during the rotation of the moving drum at a proper time in response to control signals. An inked ribbon is positioned between the type drum and a paper record upon which the data is to be printed, with the hammer striking the back of the paper record to eifect the print operation.

In such high speed printers utilizing type drums, the control system automatically distributes the printing of the characters in the proper order during each rotation so that one line of type may be printed on the record sheet for each rotation of the drum. High speeds of operation may be achieved in this manner with the usual range of such speeds being between 120 lines per minute up to approximately l,200 lines per minute to permit such high speed printers to be utilized with modern-day processing machines. such as computers or the like.

The high speed printers of the prior art have not proved entirely satisfactory in several respects. Most of such high speed printers utilize hammer assemblies of the electromechanical type wherein the energization of a solenoid causes the solenoid to strike the print hammer which, in turn, strikes the record sheet. The coupling between the solenoid armature and the print hammer may either be a direct one or through suitable linkages, but in either case, many serious problems may arise to limit the efiiciency of such devices.

It is a general object of this invention to provide a new and improved hammer assembly for a high speed printer which eliminates the problems of the prior art devices dis.- cussed above.

It is another object of this invention to provide a new and improved high speed printer having a unique hammer assembly comprised of a plurality of closely stacked dynamically operated hammers.

It is still another object of this invention to'provide a new and improved hammer assembly for a high speed printer wherein each print hammer is formed of anelongated lightweight shank having a hammer tip at oneend thereof and carrying an electrically energizable coil of wire to provide hammer movement when the coil is positioned in a suitable magnetic field.

It is still another object of this invention to provide a unique hammer assembly for a high speed printer which comprises a plurality of closely stacked lightweight print hammers each carrying an electrically energizable coil positioned for movement in a staggered array of magnet element assemblies.

It is still another object of this invention to provide a new and improved hammer assembly for high speed printers, as described, wherein each print hammer comprises an elongated shank having a hammer tip at one end thereof and carrying an electrically energizable coil in a plane parallel to the plane of the shank wherein said coil is 3,087,421 Patented Apr. 30, 1-963 2 embedded within a thin, planar sheet of plastic material.

It is still a further object of this invention to provide a new and improved high speed printer capable of operation at a speed of lines per minute upwardly with a stacking density of at least ten characters per inch.

The novel features which are characteristic of the in vention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following description taken in conjunction with the accompanying drawings in which:

FIGURE 1 is a top plan view of one particular illustrative embodiment of high speed printer embodying'the invention; 7

FIGURE 2 is a side elevational view, in cross-section, of the high speed printer taken substantially as shown along line 22 of FIGURE 1;

FIGURE 3' is a plan view of one particular embodiment of hammer and staggered magnet array in accord-v ance with the invention;

FIGURE 4' is an exploded view showing in detail the structure of a print hammer and magnet assembly em- FIGURE 9 is a top plan view, partially broken illus-- trating another alternative embodiment of staggered magnet array in accordance with this invention; and

FIGURE 10 is a top plan view of still another illustrative embodiment of staggered magnet array in accord ance with the invention.

Referring now to the drawings, and more particularly to the high speed printer shown in FIGURES 1 and 2 thereof, there is illustrated a particular embodiment of the invention which has been used with considerable success. As shown, the high speed printer 10 comprises a supporting base 12 which can take theform of a suitable casting or the like capable of supporting the elements of a high speed printer thereon. print drum 14 isoperatively coupled through a suitable bearing block 16 to a drum drive motor 18. It will be appreciated by those skilled in the art that the drum.

drive motor may be coupled to the print drum 14 either directly or through suitable gear reduction.

The print drum is provided with a suitable bearing to those skilled inthe art, and normally comprises a plu-- rality of circumferential rings of alphabetic and/or numeric characters disposed along the length of the drum,-

there being one of such rings for each printing hammer asdescribed hereinbelow. It has been found advantageous in a particular embodiment of the invention to provide a minimum of 120 columnar rings along the longitudinal extent of the print drum.

A hammer and magnet assembly 20 is positioned in operative association with print drum 14 with each print hammer being adapted, upon suitable energization, to be moved toward the print drum surface to strike a record sheet being moved between the magnet and'hammer assembly and the print drum. Advantageously, a suitable inked ribbon such as a typewriter ribbon is provided between the record sheet and the print drum for effecting An elongated the printing operation upon actuation of a printing hammer.

Thus, an inked ribbon is wound at one end thereof on the ribbon spool 24 which is adapted to rotate by means of a suitable induction or torque motor. The other end of the ribbon is Wound about a spool connected to a reversible gear motor 26, the direction of rotation of which is selectable to determine the direction of ribbon movement. While the details of the ribbon controlling means is not an important feature of this invention, nevertheless, it will be appreciated that the direction of ribbon movement may be controlled by suitable miniature switches 28 and 30 which sense the ends of the ribbon for causing a reversible direction of ribbon movement. It is contemplated that the induction or torque motor 24 will be operated continuously in a stalled condition to place a torque on the ribbon and to hold it taut. When the ribbon reaches one of its terminal ends, it is sensed by the miniature switches 28 and 30 and the reversal gear motor 26 is operated to reverse the direction of ribbon movement and causes it to be operated in the reversed direction until the opposite end of the ribbon is sensed by the miniature switches. In this manner, the ribbon is moved first in one direction until its end, and then in the other direction until its end, going back and forth during the printing operation.

It often is desirable in the utilization of print drum high speed printers to provide means for indicating the particular alpha-numerical characters on the print drum which are in operative print position to enable timing adjustments and supervision of the printing operation. Towards this end, the print drum is coupled, as by means of the shaft 32 which is rotatably journalled at the bearing member 34 and which carries at its end a disk 36 having coded holes formed therein. Those skilled in the art will appreciate that the coded holes or perforations in the disk 36 are aligned with and identify the type characters on the print drum. A source of light, such as the bulb 38, is positioned in light-transmitting relationship with a bank of photo-electric cells 40, the light source 38 being at one side of the disk 36 and the photo-cellbank 40 being positioned at the other side of the disk 36 such that the disk is intermediate the light source and photocells. Advantageously, the light beams emitted by the light source 38 may be concentrated and focused as desired by means of the concentrating lens 42 which is mounted on the bracket 44. It now can be appreciated that as the print drum 14 is rotated, the photo disk 36 rotates in a synchronous fashion to provide coded signals to the photocell bank 40 for indicating the particular type line on the drum that is coming into operative position. This permits timing adjustments of the print drum and supervision of the printing operation.

As stated hereinabove, a record sheet is caused to be passed between the hammer and magnet assembly 20 and the inked ribbon 22 so that the printing operation may be effected by causing selective hammers to strike the back of the record sheet and project it against the inked ribbon 22 and print drum 14.

In accordance with one particular embodiment of this invention, movement of the record medium may be effected by sprocket wheels or by tractor drives, either one of which comprises a plurality of spaced sprocket pins adapted to be engaged with the perforations in the record medium for transporting the record medium past the print drum at a desired rate of speed. As shown in FIGURES 1 and 2, a pair of tractor chains 50 and 52 are positioned upon a pair of spaced tractor drive wheels, such as the drive wheels 54 and 56 associated with the tractor chain 50. The tractor drive wheels for the upper portion of the record medium driving mechanism are driven by suitable drive shafts, as for example the drive: shaft 56 which is rotatably journalled at the bearings 58 and 60 and which extends beyond the bearings 60 to terminate in a pulley 62. The pulley 62 is coupled by the belt 64 to a 4 pulley 66 which is coupled to the shaft 68 of a record medium drive motor 76. It will be fully understood by those skilled in the art that the ratio of the various drive pulleys may be selected to cause the record medium drive shaft 56 to be rotated at a desired speed by the drive motor 70.

In accordance With a further feature of the high speed printer, a horizontal bar 72 is provided for enabling adjustment of the tractors to position the record medium selectively in a horizontal plane. Thus, the horizontal adjustment bar 72 is coupled to a horizontal Vernier knob 74 by means of the pulley 76, the belt 78, and the pulley 80. Rotation of the horizontal Vernier knob 74 moves the horizontal bar 72 in a right or left direction to provide horizontal adjustment of the record medium.

In addition, a vertical Vernier knob 82 is coupled through a suitable screw shaft 84 to the housing 86 of the record drive motor 70. It can be seen in FIGURE 1 that the record drive motor 70 is positioned adjacent a ramp member 88, a carrier 96, and a ball 92 which is operatively associated with the ramp 88 and carrier 90. In accordance with a feature of this invention, rotation of the vertical Vernier knob 82 causes the carrier 90 to move in either a right or left direction by virtue of the screw shaft coupling the carrier 90 to the vertical Vernier knob 82. As the carrier 90 moves, in either a right or left direction, this motion is transmitted through the ball 92 to the ramp 88. The ramp, in turn, rotates the motor housing 86 through a small angle for Vernier vertical adjustment of the record medium. It is a feature of this invention that even while the high speed printer is in operating condition, the record medium may be shifted to cause the imprinted information to agree with the preprinted data on the record medium.

It is contemplated that the high speed printer of the present invention may, if desired, be utilized with a data tape of the type well known in the data processing art. Towards this end, the drive motor 70 is coupled by means of the pulleys 94 and 96 together with their interconnecting belt 98 to a data tape shaft 100 rotatably journalled in the bracket 162. The data tape shaft 100 is coupled to the sprocket wheel 104 for enabling the data tape to be driven in a synchronous manner relative to the record medium. As understood by those skilled in the art, the data tape may comprise coded perforations adapted to be sensed by a photo-electric cell means, and this is effected by means of the light source 106 mounted on bracket 108 in light transmitting relationship with the photocells. Manifestly, the data tape means described is an optional feature for the high speed printer to provide a vertical format control to enable the programmer to move to various physical portions of the record medium.

While there has been shown and described hereinabove a specific illustrative embodiment of high speed printer, the most salient feature of the present invention is the provision of a highly unique and advantageous print hammer and magnet assembly, illustrated generally at 20 in FIGURE 1. The print hammer and magnet assembly is shown in greater detail in FIGURES 2 to 8 of the drawing and will now be described so that its unique features can be fully appreciated.

In accordance with the present invention, maximum speed of printing commensurate with minimum costs is achieved by the provision of dynamic hammer control having highly desirable electrical-to-mechanical conver sion characteristics. In general, printers operating in the desired range operate by driving the record medium forward into a continuously rotating print drum, or its equivalent, by an electrically operated hammer. Since the print drum rotates continuously, it is necessary that the print hammer be capable of rapidly imparting its energy upon the paper and then withdrawing therefrom. In order to limit smear, and other undesirable effects, the contact times generally are limited to the order of fifty microseconds. In addition, any deviation in time of striking will result in wavy rather than straight printing lines. Manifestly, it is desirable to provide proper printing that includes means for removing the excess energy of the hammer so that the hammer will return to its state of rest as quickly as possible. Further, for economical reasons, it is desirable that as little electrical energy as possible be used for the printing operation. Generally, electronic drive amplifiers are used but since they are a major item of the cost, any requirement to drive an ineflicient hammer assembly will increase their size and complexity rapidly to adversely affect the costs of construction.

In the print hammer assembly of the present invention, each hammer is analogous to a shunt D.C. linear action motor. As shown in FIGURES 2 to 8, each hammer 110 comprises an elongated shank portion 112 having :a hammer tip 114 at one end thereof and a current carrying coil 116 positioned intermediate the extreme ends of the shank.

In accordance with a feature of this invention, the current carrying coil 116 is embedded in a suitable base 118 of relatively thin planar shape such that the axis of the current carrying coil 116 is perpendicular to the plane of the base 118 and perpendicular to the longitudinal extent of the shaft 12. Advantageously, the thin planar base 118 may be formed of any metal or plastic material suitable for supporting the current carrying coil 116.

In accordance With the invention, a magnetic field is arranged so that each coil 116 is linked by two flux paths. These flux paths must be of opposite sense so that a force having the same sense is generated at both ends of the coil. As shown in FIGURES 4 and 5 in particular, the magnetic field advantageously is provided by a pair of magnet elements 120 and 122 which are positioned at opposite sides of the coil 116. It will be noted that each magnet element may be U-shaped withthe arms of the magnet element being magnetic poles of opposite polarity. The opposing magnet elements are positioned so that a south pole of one element is adjacent a north pole of the other element to provide the required flux paths;

It further will be noted that the magnet elements 120 and 122 are spaced from each other to define a gap therebetween of suflicient width to permit the current carrying coil 116 and its base member 118 to be movable in a longitudinal direction in the gap when the coil 116 is electrically energized.

With this arrangement, the force generated in the coil will be of magnitude proportional to the product of flux density, current flow, and active coil length. If the direction of current flow in the coil 116 is reversed, the force tending to move the hammer will be reversed.

Thus, in accordance with a feature of this invention, the hammer 116 can be driven forward towards the print drum by applying current in one direction to the coil 116 through the conductor leads 124 and 126, and the hammer can be withdrawn by reversing the direction of current flow through the coil 116 and conductor leads 124 and 126. When the coil 116 is in motion, the coil conductors are cutting lines of flux at the gap defined by the magnets 120 and 122.

Those skilled in the art will appreciate that this action gives rise to a back voltage of a polarity Which'tends to reduce the current in the coil. This effect has a desirable characteristic in that it is utilized in the invention to sta bilize the hammer action. Thus, if a given voltage is applied to the hammer coil 116, the hammer 110 will accelerate to such velocity that its back voltage tends to cancel the applied voltage and the net current is reduced. If the hammer movement is retarded, as by friction or the like, more current will flow causing it to accelerate back towards its required velocity. Since the velocity of the hammer is controlled by voltage, the application of zero voltage will require zero velocity and the hammer will stop. The kinetic energy contained in the hammer at the time of reducing the voltage to zero will be absorbed as electrical energy. It now can be appreciated by those 6. skilled in theart that the present inventionis. extremely desirable in that it provides for complete control of hammer actuation.

It now can be appreciated that the use of a low mass;

hammer comprising a moving coil'operating in a magnetic field. is extremely desirable for high speed printers since low costs, high: speeds, and complete control of printing It has been found advantageous to can be achieved form the hammer shank 112 of'a solid or hollow tube of a lightweight non-magnetic material such as aluminum.

As particularly shown in FIGURES'6 to 8of the drawing, the elongated tubular shank 112 is provided with a hammer tip 114 such as a block of solid aluminum, at its for-' ward end for engagement with the record medium andprint wheel. The rear end of the tubular shank 112 is provided with a pair of spaced conductors 124 and 126- which are aflixedly positionedwithin the shank 112 with respect to each other and which are insulated from each other by means of the insulating strips 128 and 1 30 providedi at the interior side walls of shank 112, as particularly shown in FIGURES 6 and 7 of the drawing.

The current carrying coil 116 is embedded or encapsul-ated' in a suitable manner, in the base planar member 11 8, as illustrated in FIGURE 6, and the terminal ends of the current carrying coil 116 are connected respectively to the conductors 1-24 and 126. Itnow can befullly appreciated that the axis of current carrying coil 116 is perpendicularto the plane of base 118 and is perpendicular to the direction of movement of hammer in the .gap defined by the magnet elements and 122.

Another important feature of the present invention is the high stacking density which can be achieved by the dynamic print hammers described hereinabove. Printing,

as normally done with business and other data processing machines, requires that the characters be spaced on .1 inch centers. Thus, this requires that the hammers also be spaced on .1 inchv centers. In accordance with a feature of this invention, this stacking density is achieved by the provision of a staggered array of magnet element pairs. One row in the array is illustrated in FIGURE 5 of the drawing and it can there be seen how six closely stacked.

mer would be staggered, moving from the tip end of thehammer towards the rear end of the hammer, so that thecoil-s would be movably positioned Within the gaps of their respectively associated magnets. Movement of each current carrying coil 116 in the gap of its magnet element pair is facilitated by the guides 132 and 134 located at each end of the hammer. The guides are provided with suitable slots 136-, there being one slot for each hammer, to provide the proper spacing between the hammers and to insure the linear movement of each hammer without interference with the adjacent hammer on either side thereof. Since the slots 136 in the guides 132 and 134 are arranged on .1 inch centers, the desired stacking denslty and spacing for the hammers can be rigidly controlled.

Reference is now made to FIGURE 3 of the drawing which illustrates an array of staggered magnet element pairs, there being six of such magnet element pairs in each row. If, in accordance with general practice, it is desirable to provide a minimum of 120 columnar portions for the printer, then twenty rows, each having six staggered magnet element pairs, may be provided in the magnet array. The slotted guides 132 and 134 are provided at the forward and rear portions of the sub-strate 140 containing the magnet element pairs for guiding the movement of the various hammers 110' relative to the rotating type drum 14.

Advantageously, the magnet element pairs may be attached, as by a suitable adhesive, epoxy, weld or the like, to a sub-strate 140 of non-magnetic material. The slotted guides 132 and 134 may advantageously be formed of molded plastic which is attached to the front and back walls of the non-magnetic frame. As shown in FIGURE 3, and particularly by the arrows 142, the magnetic flux paths of the magnet element pairs is such as to minimize magnetic interaction between adjacent magnetic element pairs while at the same time providing the desired linkage of each coil by two flux paths.

An alternative embodiment of magnet element array is shown in FIGURE 9 of the drawing. It can there be seen that the modified magnet element array comprises a plurality of staggered magnet elements 150, which are staggered to permit close stacking of the magnet hammers in the manner described hereinabove. For example, the current carrying coil 152 is shown as positioned within the slotted gap defined by the adjacent magnets, and the current carrying coil 154 is positioned in a slotted gap which is in staggered relationship with respect to the coil 152. The flux paths in this assembly may take the form shown by the arrows 156 wherein the magnet elements are treated as long bars and are magnetized so that the flux flows from one side of the magnet array to the other and then back to the first side. In order to reduce linkage between such long bars it will be noted that the flux pattern is reversed to place similar poles in close proximity and to cause the flux lines to be mutually repelled.

Still another embodiment of the invention is shown in FIGURE 10 of the drawing wherein the pole piece elements 158 and 160, of difierent configuration, are utilized in conjunction with a large C-shaped permanent magnet 162. The pole piece elements 158 and 169 are mounted on a non-magnetic sub-strate 164 which is bounded by the large permanent magnet having a north pole at the arm 166 thereof and a south pole at the arm 168 thereof. In this magnetic array, the slotted gaps between the pole piece elements are staggered as illustrated by the movable current carrying coils 170 and 172' of adjacent print hammers. The magnetic flux path for this magnet array is illustrated by the arrows 174. It has been found with this type of an array having an external magnet 162 and the pole pieces 158 and 160 to deflect the flux paths in the required flux pattern produces very high flux density of 10,000 to 11,000 gauss.

There has been shown and describe-d hereinabove a unique and highly advantageous high speed printing apparatus which is characterized by a unique print hammer and magnet assembly. Each print hammer is characterized by its low mass and by its dynamic operation in that it carries with it a coil of wire adapted to be energized in the magnet assembly to provide the desired movement Of the print hammer. It is contemplated that the hammers can be stacked with their cores alternately above and below the shaft center line in the printer to permit printsing of one or two lines at a time.

Obviously, in printing two lines at a time, the printing speed can be doubled with a very high packing density without requiring additional non-working memory for the data processing apparatus.

It further is contemplated in a practical embodiment of the invention, that the printing hammer will have a travel of approximately .200 inch with the advantage of less critical tolerances in the axis of movement. When energized, each hammer coil of approximately fifty turns can handle three amperes of current flow so that such printing hammers could be used to punch or perforate a record medium in addition to printing on the same.

While there has been shown and described a specific embodiment of the present invention, it will, of course, be understood that various modifications and alternative constructions may be made without departing from the true spirit and scope of the invention. Therefore, it is intended by the appended claims to cover all such modifications and alternative constructions as fall within their true spirit and scope.

What is claimed as the invention is:

l. The improvement of high speed printing apparatus comprising the combination of type bearing means having a plurality of printing characters distributed thereon, a plurality of dynamic printing hammers positioned in operative association with said type bearing means, each of said printing ham-mers comprising a low mass, elongated shank having a hammer tip extending from one end, a pair of conductors extending from the other end and an electrically energizable current carrying coil located on said shank intermediate said ends, said current carrying coil being embedded in a thin planar base of material such that the axis of said coil is perpendicular to the plane of said base and to the longitudinal extent of said shank, and magnetic means for providing a magnetic field to enable a printing hammer having its coil energized to be moved relative to said type bearing means for printing selected ones of said characters, said magnetic means comprising a magnetic element pair for each printing hammer, said magnetic element pairs being disposed in a staggered array, each of said pairs including two magnetic pole pieces spaced from each other to define a slot-shaped gap therebetween adapted to receive a current carrying coil of one printing hammer therein for guiding the relative movement of the hammer upon energization of the coil.

2. The improvement of high speed printing apparatus comprising the combination of type bearing means having a plurality of printing characters distributed thereon, a plurality of dynamic printing hammers positioned in operative association with said type bearing means, each of said printing hammers comprising an elongated shank having a hammer tip at one end, a pair of conductors at the other end and an electrically energizable current carrying coil located on said shank intennedi ate said ends, the axis of said coil being perpendicular to the longitudinal extent of said shank, and magnetic means for providing a magnetic field to enable a printing hammer having its current carrying coil energized to be moved relative to said type bearing means for printing selected ones of said characters, said magnetic means comprising :a magnetic element pair for each printing hammer, said magnetic element pairs being disposed in a staggered array, the elements of each pair being spaced from each other to define a slot-shaped gap therebetween adapted to receive a current carrying coil of one printing hammer therein for guiding the relative movement of the hammer upon energization of the coil.

3. The improvement of high speed printing apparatus comprising the combination of a rotatable type drum having a plurality of printing characters distributed around the periphery of said drum, a plurality of dynamic printing hammers positioned in operative association with said drum, each of said printing hammers comprising an elongated shank having an electrically energizable current carrying coil located intermediate the ends of the shank, the aXis of said coil being perpendicular to the longitudinal extent of said shank, and magnetic means for providing a magnetic field to cause those of said printing hammers having excited coils .to be moved relative to said type drum for printing selected ones of said characters, said magnetic means comprising an array of staggered magnetic elements, pairs of said elements being spaced from each other to define a slot-shaped gap therebetween adapted to receive a current carrying coil of a printing hammer therein for guiding the relative movement of the hammer upon energization of the coil.

4. The improvement of high speed printing apparatus comprising the combination of movable type bearing means having a plurality of printing characters distributed thereon, a plurality of dynamic printing hammers positioned in operative association with said type bearing means, each of said printing hammers comprising an elongated shank having an electrically energizable current earring coil located intermediate the ends of said shank with its axis positioned perpendicular to the longitudinal extent of said shank, and magnetic means for providing a magnetic field to cause those of said printring hammers having excited coils to be moved relative to said type bearing means for printing selected ones f said characters, said magnetic means compriting an array of staggered magnetic element pairs, each of said pairs including two magnetic elements spaced from each other to define a slot-shaped gap therebetween adapted to receive a current carrying coil of one printing hammer therein for guiding the relative movement of the hammer upon energization of the coil.

5. The improvement of high speed printing apparatus in accordance with claim 4 wherein said magnetic element pairs are arranged with like poles adjacent each other in adjacent pairs to minimize interaction by eliminating flux linkage between adjacent flux fields.

6. The improvement of high speed printing apparatus comprising the combination of movable type bearing means having a plurality of printing characters distributed thereon, :a plurality of dynamic printing hammers positioned in operative association with said type bearing means, each of said printing hammers comprising an elongated shank having a hammer tip at one end and an electrically energizable current earring coil located int rmediate the shank ends, the axis of said coil being perpendicular to the longitudinal extent of said shank, and magnetic means for providing a magnetic field to enable those of said printing hammers having an energized coil to be moved relative to said type bearing means for printing selected ones of said characters, said magnetic means comprising an array of staggered magnetic element pairs, each of said pairs including two magnetic elements spaced from each other to define a slot-shaped gap therebetween adapted to receive a current carrying coil of a printing hammer therein for guiding the relative movement of the hammer upon energization of the coil, the flux field of each pair of magnetic elements being perpendicular to the plane of the coil so that the turns of each coil are linked by two flux paths.

-7. A dynamic print hammer for use in high speed printing apparatus comprising a low mass, elongated shank having a hammer tip extending from one end, a pair of conductors extending from the other end and an electrically energizable current earring coil located on said shank intermediate said ends, said current carrying coil being embedded in a thin planar base material such that the axis of said coil is perpendicular to the plane of said base and to the longitudinal extent of said shank.

8. A dynamic print hammer for use in high speed printing apparatus comprising a low mass, elongated shank of light weight tubular material, a solid hammer tip extending from one end of said shank, a pair of conductors extending from the other end of said shank, and an electrically energizable current carrying coil located on said shank intermediate said ends and connected to said pair of conductors, said current carrying coil being embedded in a thin planar base of material such that the axis of said coil is perpendicular to the plane of said base and to the longitudinal extent of said shank.

References Cited in the file of this patent UNITED STATES PATENTS 723,119 Von Zweigbergk Mar. 17, 1903 1,871,446 Decker Aug. 16, 1932 2,640,955 Fisher June 2, 1953 2,787,210 Shepard Apr. 2, 1957 2,843,243 Masterson July 15, 1958 2,858,536 Johnston Oct. 28, 1958 2,640,955 DeVilliers Oct. 25, 1960 2,976,801 Dirks Mar. 28, 1961 

1. THE IMPROVMENT OF HIGH SPEED PRINTING APPARATUS COMPRISING THE COMBINATION OF TYPE BEARING MEANS HAVING A PLURALITY OF PRINTING CHARACTERS DISTRIBUTED THEREON, A PLURALITY OF DYNAMIC PRINTING HAMMERS POSITIONED IN OPERATIVE ASSOCIATION WITH SAID TYPE BEARING MEANS, EACH OF SAID PRINTING HAMMERS COMPRISING A LOW MASS, ELONGATED SHANK HAVING A HAMMER TIP EXTENDING FROM ONE END, A PAIR OF CONDUCTORS EXTENDING FROM THE OTHER END AND AN ELECTRICALLY ENERGIZABLE CURRENT CARRYING COIL LOCATED ON SAID SHANK INTERMEDIATE SAID ENDS, SAID CURRENT CARRYING COIL BEING EMBEDDED IN A THIN PLANAR BASE OF MATERIAL SUCH THAT THE AXIS OF SAID COIL IS PERPENDICULAR TO THE PLANE OF SAID BASE AND TO THE LONGITUDINAL EXTENT OF SAID SHANK, AND MAGNETIC MEANS FOR PROVIDING A MAGNETIC FIELD TO ENABLE A PRINTING HAMMER HAVING ITS COIL ENERGIZED TO BE MOVED RELATIVE TO SAID TYPE BEARING MEANS FOR PRINTING SELECTED ONES OF SAID CHARACTERS, SAID MAGNETIC MEANS COMPRISING A MAGNETIC ELEMENT PAIR FOR EACH PRINTING HAMMER, SAID MAGNETIC ELEMENT PAIRS BEING DISPOSED IN A STAGGERED ARRAY, EACH OF SAID PAIRS INCLUDING TWO MAGNETIC POLE PIECES SPACED FROM EACH OTHER TO DEFINE A SLOT-SHAPED GAP THEREBETWEEN ADAPTED TO RECEIVE A CURRENT CARRYING COIL OF ONE PRINTING HAMMER THEREIN FOR GUIDING THE RELATIVE MOVEMENT OF THE HAMMER UPON ENERGIZATION OF THE COIL. 